TPE don't do power changeovers on the move currently (quite aside from the capability, or otherwise, of the wiring to withstand moving pantographs being raised). Nothing stopping the pan from being raised whilst at Piccadilly but it would be a bit pointless as most of the turnarounds are only 20-25 mins and the diesel engines need to be restarted in time for departure.
Guide Bridge-Stalybridge is certainly in the last version of the plan I've seen - the bigger omission IMHO is Philips Park West Jn to Ashburys, which is a very useful little line that's currently slated to remain unelectrified.
Ah yes, that small line that goes to / from Miles Platting. I agree, it would make sense if that bit was also electrified.
I wonder if the reason it's omitted (or not considering) is because it's lack of passenger train use (only freight / ECS)?
I seem to remember that there was a once a week TPE service to Manchester Victoria / Liverpool that went that way I think for route knowledge (Sunday only) on the May 18 / pre-Covid timetable.
Sadly this service no longer exists now.